Heat transfer systems are used to transport heat from one location (the heat source) to another location (the heat sink). Heat transfer systems can be used in terrestrial or non-terrestrial applications. For example, heat transfer systems can be used in electronic equipment, which often require cooling during operation. Heat transfer systems can also be used in, and integrated with, satellite equipment that operates within zero- or low-gravity environments.
Loop Heat Pipes (LHPs) and Capillary Pumped Loops (CPLs) are examples of passive two-phase loop heat transfer systems. Each includes an evaporator thermally coupled to the heat source, a condenser thermally coupled to the heat sink, fluid that flows between the evaporator and the condenser, and a fluid reservoir for accommodating redistribution or volume changes of the fluid and for heat transfer system temperature control. The fluid within the heat transfer system can be referred to as the working fluid. The evaporator includes a wick that enables liquid flow. Heat acquired by the evaporator is transported to and rejected by the condenser. These systems utilize capillary pressure developed in a fine-pored wick within the evaporator to promote circulation of working fluid from the evaporator to the condenser and back to the evaporator.